CN102214931B - Device and method for low voltage ride through of double-fed inductive wind power generator system - Google Patents

Abstract

The invention discloses a device and method for low voltage ride through of a double-fed inductive wind power generator system. In the invention, the advantages of using a high-resistance resistor and a low-resistance resistor are effectively combined through the real-time regulation of the equivalent resistance of a crowbar resistor; under the condition of small voltage fluctuation of a direct-current bus, the shock of rotor current is better inhibited, and the rotor current is quickly attenuated to a safe range, so that a rotor excitation converter is effectively protected and the transient-state shock to an electrical network and a mechanical system is reduced; meanwhile, security, stability and recovery of the voltage of the electrical network are effectively aided through the cooperative reactive power compensation of a rotor side converter and a network side converter during the voltage dip of the electrical network.

Description

The method that double-fed induction wind driven generator system low-voltage passes through

Technical field

The invention belongs to generation of electricity by new energy technical field, relate in particular to the device and method that a kind of double-fed induction wind driven generator system low-voltage passes through.

Background technology

Along with the continuous expansion in China's wind power generation market, wind power generation proportion in electric power system rises year by year, and its impact for electrical network be can not ignore.Therefore, countries in the world have proposed to possess the requirement of low voltage ride-through capability to wind generator system, necessarily fall in scope at line voltage, wind-driven generator must keep being connected with electrical network, and wants to provide certain reactive power (voltage) to support to electrical network.Double-fed induction wind driven generator (Doubly-Fed Induction Generator, be called for short DFIG) is because its frequency inverter capacity is little, and can realize the advantages such as decoupling zero control to active power and reactive power, is widely used in wind generator system.

But, because double-fed induction wind driven generator stator is directly connected with electrical network, in the time that line voltage falls, can produce very large transient current in rotor side, simultaneously because wind energy conversion system governing speed is slower, and line voltage is now lower, the energy that cannot be transported to electrical network can cause dc-link capacitance quick charge to make DC bus-bar voltage increase rapidly.The normal operation of this electromagnetic transient meeting serious threat double-fed induction wind driven generator system.Therefore, the low voltage ride-through capability of research double-fed induction wind driven generator in electric network fault situation becomes when last large focus.

Existing literature research shows; in electric network fault situation; rely on improvement control strategy to play a role to a certain extent; but due to the restriction of the factors such as converter capacity and the parameter of electric machine; once comparatively serious voltage occurs to be fallen; the improvement of simple dependence control strategy is difficult to realize low voltage crossing, must increase hardware auxiliary circuit, and the conventional crow bar of the use protection (Crowbar Protection) that has is installed.A lot of documents have all been considered the impact of crow bar resistance on double-fed induction wind driven generator group low voltage ride-through capability.Put it briefly, first, crow bar resistance is larger, and the maximum current of rotor is just less, therefore when first the design of crow bar resistance will meet electrical network low voltage generation, the maximum of rotor current is less than the safe current that device allows, and can obtain thus the minimum resistance of crow bar resistance; Secondly; if crow bar resistance is too little; can protect in course of action and by backward diode, the dc-link capacitance in rotor-exciting converter be charged at crow bar; cause the too high and then harm converter safety of DC bus-bar voltage; therefore the ohmically voltage of crow bar should be less than the maximum voltage value that DC bus can bear, and can calculate thus the maximum of crow bar resistance.In summary, the selection of crow bar resistance need meet following two conditions:

A. maximum transient state stator and rotor current when resistance needs enough to occur with fault restriction greatly,

B. resistance needs enough little too high to prevent that DC bus-bar voltage from rising to.

The impact of crow bar resistance is most important in low voltage crossing process, but not yet has document to provide the scheme of suitable definite crow bar resistance.Therefore; in the research of double-fed induction wind driven generator system low-voltage crossing technology; extremely be necessary to optimize existing crow bar protective device topological structure; choose suitable crow bar resistance, and carry out effective low voltage crossing flow arrangement to guarantee aerogenerator unit safe and to assist as much as possible fault power system restoration.

Summary of the invention

A kind of method that provides double-fed induction wind driven generator system low-voltage regulating in real time based on crow bar resistance to pass through is provided for the deficiencies in the prior art.

The object of the invention is to be achieved through the following technical solutions:

A kind of method that double-fed induction wind driven generator system low-voltage passes through, on the device that the method is passed through at double-fed induction wind driven generator system low-voltage, realize, the device that described double-fed induction wind driven generator system low-voltage passes through is mainly made up of double-fed induction wind driven generator, rotor-exciting converter, crow bar protective device, du/dt inductance, LCL filter and system controller; Wherein, the rotor three-phase winding of double-fed induction wind driven generator is connected with rotor-exciting converter one side by du/dt inductance, and the opposite side of rotor-exciting converter is connected to electrical network by LCL filter and grid-connected transformer; The three-phase input end of crow bar protective device is connected with the rotor three-phase winding of double-fed induction wind driven generator by du/dt inductance, on connecting, forms relation in parallel with rotor-exciting converter; System controller is connected with crow bar protective device with rotor-exciting converter; Rotor-exciting converter is made up of grid side converter, dc-link capacitance and rotor-side converter; The method comprises the following steps:

(1) in the time that electrical network low voltage causes double-fed induction wind driven generator rotor current to rise to being equal to or greater than capping value, system controller blocks rotor-side converter pulses conducting crow bar protective device switch, drop into crow bar protective device, the active power instruction of rotor-side converter is made as to zero simultaneously, and the input of rotor current ring pi regulator integration item is made as to zero;

(2) after crow bar protective device switch conduction, grid side converter is meeting outside necessary active power demand, and trying one's best provides reactive power support to electrical network; Simultaneously by the real-time adjusting to crow bar equivalent resistance resistance, fluctuate little in the situation that in DC bus-bar voltage, restrain preferably the impact of rotor current, and make quickly rotor current decay in safe range, thereby obtain comparatively ideal low voltage crossing performance;

(3) when double-fed induction wind driven generator rotor current decays to while being less than or equal to preset lower limit, system controller turn-offs crow bar protective device switch and excises crow bar protective device, open rotor-side converter pulses simultaneously, rotor-side converter is resumed work and rapidly for electrical network provides certain reactive power, is assisted power system restoration;

(4) line voltage recover and crow bar protective device cut after; the input of rotor current ring pi regulator integration item is reverted to the difference of instruction current and feedback current; grid side converter slowly recovers rated reactive power instruction; rotor-side converter slowly recovers rated reactive power instruction and active power instruction simultaneously, and system is recovered specified running status subsequently.

Further, described step (2) realizes by following sub-step:

(2.1) according to the specified rotor current amplitude of double-fed induction wind driven generator system and the maximum DC bus-bar voltage that allows, determine the function f that is respectively take three-phase rotor current maximum amplitude and DC bus-bar voltage as variable (| I _r| _max) and f (V _dc);

Function f (| I _r| _max) and f (V _dc) be respectively | I _r| _maxand V _dcpositive relationship linear function and the negative linear function that is related to,

$f\left({\left|I_r\right|}_{\max }\right)=\frac{{\left|I_r\right|}_{\max }-I_N}{I_N}$

$f\left(V_{\mathrm{dc}}\right)=\frac{V_{\mathrm{dc}\_\mathrm{safe}}-V_{\mathrm{dc}}}{V_N};$

Wherein, | I _r| _maxfor the maximum of the three-phase rotor current signal recording from du/dt inductance and rotor-exciting converter link taking absolute value respectively, i.e. three-phase rotor current maximum amplitude, I _nfor specified rotor current amplitude, V _{dc_safe}for maximum allows DC bus-bar voltage, V _dcfor the DC bus-bar voltage recording from rotor-exciting converter dc-link capacitance two ends, V _nfor specified DC bus-bar voltage;

(2.2) adopt weighting method to function f (| I _r| _max) and f (V _dc) carry out comprehensive calculation process, obtain becoming resistance signal;

Becoming resistance signal can be obtained by following formula:

$\begin{array}{c}\mathrm{\η}=f({\left|I_r\right|}_{\max },V_{\mathrm{dc}})=\mathrm{\α}\×f\left({\left|I_r\right|}_{\max }\right)+(1-\mathrm{\α})\×f\left(V_{\mathrm{dc}}\right)\\ =\mathrm{\α}\×\frac{{\left|I_r\right|}_{\max }-I_N}{I_N}+(1-\mathrm{\α})\×\frac{V_{\mathrm{dc}\_\mathrm{safe}}-V_{\mathrm{dc}}}{V_N}\end{array};$

Wherein, α is the weight coefficient of considering rotor current impact;

(2.3) result above-mentioned power transformation resistance calculated signals formula being obtained is done output violent change, and then obtain equivalent crow bar resistance, realize the real-time adjusting of crow bar resistance: power transformation is hindered to the result that calculated signals formula obtains and do output violent change, bottoming value is 0, output higher limit is 1, obtains final for calculating the change resistance signal η of equivalent crow bar resistance ₀, and then obtain equivalent crow bar resistance R _cBresistance be:

R _CB=R ₀+η ₀×R ₁；

Wherein, crow bar resistance is by resistance R ₀with the resistance R that is parallel with chopper ₁resistance branch in series, it is as follows that its resistance is chosen process:

First when, first the design of crow bar resistance will meet fault generation, the maximum of rotor current is less than the safe current I that device allows _safe, that is:

$\frac{{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_1}\frac{U_s}{\sqrt{{\left({\mathrm{\&omega;}}_r{L}_{\mathrm{\&sigma;}}\right)}^2+{\mathrm{<figure-callout\; id="2"\; label="R\; CB"\; filenames="110523134913.png,110523135116.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{CB}}^{}}}<I_{\mathrm{safe}};$

Formula can calculate crow bar resistance R thus _cBminimum value R _cBmin, that is:

$R_{\mathrm{CB}\min }=\frac{{\mathrm{\&omega;}}_r}{I_{\mathrm{safe}}}\sqrt{{\left(\frac{U_s}{{\mathrm{\&omega;}}_1}\right)}^2-{\left(L_{\mathrm{\&sigma;}}{I}_{\mathrm{safe}}\right)}^2}\text{;}$

Secondly, the ohmically voltage of crow bar should be less than the magnitude of voltage V that DC bus can bear _{dc_safe}, that is:

$\frac{{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_1}\frac{\sqrt{3}{R}_{\mathrm{CB}}{U}_s}{\sqrt{{\left({\mathrm{\&omega;}}_r{L}_{\mathrm{\&sigma;}}\right)}^2+{\mathrm{<figure-callout\; id="2"\; label="R\; CB"\; filenames="110523134913.png,110523135116.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{CB}}^{}}}<V_{\mathrm{dc}\_\mathrm{safe}};$

Formula can calculate crow bar resistance R thus _cBmaximum R _cBmax:

$R_{\mathrm{CB}\max }=\frac{V_{\mathrm{dc}\_\mathrm{safe}}{\mathrm{\&omega;}}_r{L}_{\mathrm{\&sigma;}}}{\sqrt{3{(U_s{\mathrm{\&omega;}}_r/{\mathrm{\&omega;}}_1)}^2-V_{\mathrm{dc}\_\mathrm{safe}}^2}};$

In above-mentioned four formulas, L _σ=L _{σ s}+ L _{σ r}for single-phase total leakage inductance, L _{σ s}, L _{σ r}be respectively stator phase leakage inductance and rotor phase leakage inductance, U _sfor stator phase voltage peak value, ω _r, ω ₁be respectively rotor speed angular velocity of rotation and synchronous rotary angular speed;

By resistance R ₀be taken as crow bar resistance R _cBminimum value R _cBmin, by resistance R ₁be taken as crow bar resistance R _cBmaximum and the difference of minimum value, i.e. R ₀=R _cBmin, R ₁=R _cBmax-R _cBmin; Now, crow bar resistance can be got in theory from R _cBminto R _cBmaxdifferent value.

The present invention compared with prior art, its effective effect is: the present invention is by the real-time adjusting of crow bar equivalent resistance resistance, effectively combine and use large value resistance and the advantage that uses little value resistance, can fluctuate little in the situation that in DC bus-bar voltage, restrain preferably the impact of rotor current, and quickly rotor current is decayed in safe range, effectively protect rotor-exciting converter, reduce the transient state of electrical network and mechanical system has been impacted; The collaborative reactive power compensation of rotor-side converter and grid side converter during simultaneously falling by line voltage, has effectively assisted safety and stability and the recovery of line voltage.

Accompanying drawing explanation

Fig. 1 is equipped with the initiatively double-fed induction wind driven generator system architecture diagram of crow bar protective device;

Fig. 2 is the active crow bar protective device that crow bar resistance regulates in real time;

The control flow chart of double-fed induction wind driven generator system when Fig. 3 is low voltage crossing;

The operational effect figure of the stator voltage of the double-fed induction wind driven generator of employing the inventive method when Fig. 4-Figure 10 is respectively low voltage crossing, stator current, rotor current, DC bus-bar voltage, stator side active power, stator side reactive power, electromagnetic torque;

When Figure 11-Figure 13 is respectively low voltage crossing, adopt fixing little value crow bar resistance, the operational effect figure of three-phase rotor current maximum amplitude, electromagnetic torque, DC bus-bar voltage;

When Figure 14-Figure 16 is respectively low voltage crossing, adopt fixing large value crow bar resistance, the operational effect figure of three-phase rotor current maximum amplitude, electromagnetic torque, DC bus-bar voltage;

When Figure 17-Figure 19 is respectively low voltage crossing, adopt resistance of the present invention to regulate in real time crow bar resistance, the operational effect figure of three-phase rotor current maximum amplitude, electromagnetic torque, DC bus-bar voltage.

Embodiment

Describe with reference to the accompanying drawings the present invention below in detail, it is more obvious that object of the present invention and effect will become.

1. the structure of double-fed induction wind driven generator system low-voltage traversing device

Referring to Fig. 1, the double-fed induction wind driven generator system of this outfit crow bar protective device is by double-fed induction wind driven generator, rotor-exciting converter, crow bar protective device, du/dt inductance, LCL filter and system controller composition.

The rotor three-phase winding of double-fed induction wind driven generator is connected with rotor-exciting converter one side by du/dt inductance, and the opposite side of rotor-exciting converter is connected to electrical network by LCL filter and grid-connected transformer.The three-phase input end of crow bar protective device is connected with the rotor three-phase winding of double-fed induction wind driven generator by du/dt filter, on connecting, forms relation in parallel with rotor-exciting converter.System controller is connected with crow bar protective device with rotor-exciting converter.Rotor-exciting converter is made up of grid side converter, dc-link capacitance and rotor-side converter.

Double-fed induction wind driven generator system low-voltage traversing device be crow bar protective device as shown in Figure 2.The three-phase input end of crow bar protective device is connected with du/dt inductance link with rotor-side converter, has guaranteed the realization of double-fed induction wind driven generator group low voltage crossing.Crow bar protective device comprises that three-phase do not control rectifier bridge, crow bar resistance and switch.It is the not control rectifying circuit of full-bridge type that heavy-duty diode forms that three-phase is not controlled rectifier bridge.Crow bar resistance is by resistance R ₀with the resistance R that is parallel with chopper ₁resistance branch in series, resistance R ₀resistance be less than resistance R ₁.The positive output end that three-phase is not controlled rectifier bridge is connected with one end of crow bar resistance, and the negative output terminal that the other end of crow bar resistance is not controlled rectifier bridge by switch with three-phase is connected.Switch is responsible for the input of crow bar protective device and is cut out, and switch can be full-control type turn-off device (as IGBT), but is not limited to this.With resistance R ₁chopper in parallel can be made up of full-control type turn-off device, but is also not limited to this.Crow bar protective device is controlled by system controller, and as shown in Figure 1, chopper is all connected with system controller with switch.Rotor current signal and DC bus-bar voltage signal are carried out comprehensive computing by system controller, output two paths of signals, crow bar control signal is given the switch of described crow bar protective device, become resistance signal in crow bar protective device with resistance R ₁chopper in parallel.

2. the method that double-fed induction wind driven generator system low-voltage passes through

As shown in Figure 3, the method that double-fed induction wind driven generator system low-voltage passes through is as follows:

1, in the time that electrical network low voltage causes double-fed induction wind driven generator rotor current to rise to being equal to or greater than capping value, system controller blocks rotor-side converter pulses conducting crow bar protective device switch, drop into crow bar protective device, the active power instruction of rotor-side converter is made as to zero simultaneously, and the input of rotor current ring pi regulator integration item is made as to zero;

2, after crow bar protective device switch conduction, grid side converter is meeting outside necessary active power demand, and trying one's best provides reactive power support to electrical network; Simultaneously by the real-time adjusting to crow bar equivalent resistance resistance, can fluctuate little in the situation that in DC bus-bar voltage, restrain preferably the impact of rotor current, and make quickly rotor current decay in safe range, thereby obtain comparatively ideal low voltage crossing performance;

3, when decaying to, double-fed induction wind driven generator rotor current is less than or equal to preset lower limit, system controller turn-offs crow bar protective device switch and excises crow bar protective device, open rotor-side converter pulses simultaneously, rotor-side converter is resumed work and rapidly for electrical network provides certain reactive power, is assisted power system restoration;

4, line voltage recover and crow bar protective device cut after; the input of rotor current ring pi regulator integration item is reverted to the difference of instruction current and feedback current; grid side converter slowly recovers rated reactive power instruction; rotor-side converter slowly recovers rated reactive power instruction and active power instruction simultaneously, and system is recovered specified running status subsequently.

The implementation procedure below crow bar equivalent resistance resistance in above-mentioned steps 2 being regulated is in real time elaborated as follows:

1. according to the specified rotor current amplitude of double-fed induction wind driven generator system and the maximum DC bus-bar voltage that allows, determine the function f that is respectively take three-phase rotor current maximum amplitude and DC bus-bar voltage as variable (| I _r| _max) and f (V _dc);

Function f (| I _r| _max)and f (V _dc) be respectively | I _r| _maxand V _dcpositive relationship linear function and the negative linear function that is related to,

$f\left({I_r}_{\max }\right)=\frac{{\left|I_r\right|}_{\max }-I_N}{I_N}$

$f\left(V_{\mathrm{dc}}\right)=\frac{V_{\mathrm{dc}\_\mathrm{safe}}-V_{\mathrm{dc}}}{V_N};$

Wherein, | I _r| _maxfor the maximum of the three-phase rotor current signal recording from du/dt inductance and rotor-exciting converter link taking absolute value respectively, i.e. three-phase rotor current maximum amplitude, I _nfor specified rotor current amplitude, V _{dc_safe}for maximum allows DC bus-bar voltage, V _dcfor the DC bus-bar voltage recording from rotor-exciting converter dc-link capacitance two ends, V _nfor specified DC bus-bar voltage.

Adopt weighting method to function f (| I _r| _max)and f (V _dc) carry out comprehensive calculation process, obtain becoming resistance signal;

Becoming resistance signal can be obtained by following formula:

$\begin{array}{c}\mathrm{\&eta;}=f({\left|I_r\right|}_{\max },V_{\mathrm{dc}})=\mathrm{\&alpha;}\&times;f\left({\left|I_r\right|}_{\max }\right)+(1-\mathrm{\&alpha;})\&times;f\left(V_{\mathrm{dc}}\right)\\ =\mathrm{\&alpha;}\&times;\frac{{\left|I_r\right|}_{\max }-I_N}{I_N}+(1-\mathrm{\&alpha;})\&times;\frac{V_{\mathrm{dc}\_\mathrm{safe}}-V_{\mathrm{dc}}}{V_N}\end{array};$

Wherein, α is the weight coefficient of considering rotor current impact.

Above formula uses one with three-phase rotor current maximum amplitude | I _r| _maxwith DC bus-bar voltage V _dcfor the function f of variable quantity (| I _r| _max, V _dc) calculate change resistance signal η, so the duty ratio m of definite chopper, m=1-η.Weight coefficient α does corresponding adjustment in 0～1 scope according to actual requirement, to obtain the control effect of expectation, that is, if the requirement that system suppresses rotor current is higher, weight coefficient α can be obtained relatively large; If system is higher to DC bus-bar voltage restriction requirement, can weight coefficient α be obtained relatively little.Generally speaking, because dc-link capacitance capacity is larger, DC bus-bar voltage is compared rotor current variation and is wanted much slow, therefore, controls rotor current variation and seems even more important, therefore α span is generally 0.5～1.

3. the result above-mentioned power transformation resistance calculated signals formula being obtained is done output violent change, and then obtains equivalent crow bar resistance, realizes the real-time adjusting of crow bar resistance.

Power transformation is hindered to the result that calculated signals formula obtains and do output violent change, bottoming value is 0, and output higher limit is 1, obtains final for calculating the change resistance signal η of equivalent crow bar resistance ₀, and then obtain equivalent crow bar resistance R _cBresistance be

R _CB=R ₀+η ₀×R ₁。

Wherein, R ₀, R ₁with the relation of crow bar resistance as shown in Figure 2, it is as follows that its resistance is chosen process:

First when, first the design of crow bar resistance will meet fault generation, the maximum of rotor current is less than the safe current I that device allows _safe,

$\frac{{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_1}\frac{U_s}{\sqrt{{\left({\mathrm{\&omega;}}_r{L}_{\mathrm{\&sigma;}}\right)}^2+{\mathrm{<figure-callout\; id="2"\; label="R\; CB"\; filenames="110523134913.png,110523135116.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{CB}}^{}}}<I_{\mathrm{safe}};$

Formula can calculate crow bar resistance R thus _cBminimum value R _cBmin, that is:

$R_{\mathrm{CB}\min }=\frac{{\mathrm{\&omega;}}_r}{I_{\mathrm{safe}}}\sqrt{{\left(\frac{U_s}{{\mathrm{\&omega;}}_1}\right)}^2-{\left(L_{\mathrm{\&sigma;}}{I}_{\mathrm{safe}}\right)}^2}\text{;}$

Secondly, the ohmically voltage of crow bar should be less than the magnitude of voltage V that DC bus can bear _{dc_safe}, that is:

$\frac{{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_1}\frac{\sqrt{3}{R}_{\mathrm{CB}}{U}_s}{\sqrt{{\left({\mathrm{\&omega;}}_r{L}_{\mathrm{\&sigma;}}\right)}^2+{\mathrm{<figure-callout\; id="2"\; label="R\; CB"\; filenames="110523134913.png,110523135116.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{CB}}^{}}}<V_{\mathrm{dc}\_\mathrm{safe}};$

Formula can calculate crow bar resistance R thus _cBmaximum R _cBmax:

$R_{\mathrm{CB}\max }=\frac{V_{\mathrm{dc}\_\mathrm{safe}}{\mathrm{\&omega;}}_r{L}_{\mathrm{\&sigma;}}}{\sqrt{3{(U_s{\mathrm{\&omega;}}_r/{\mathrm{\&omega;}}_1)}^2-V_{\mathrm{dc}\_\mathrm{safe}}^2}};$

In above-mentioned four formulas, L _σ=L _{σ s}+ L _{σ r}for single-phase total leakage inductance, L _{σ s}, L _{σ r}be respectively stator phase leakage inductance and rotor phase leakage inductance, U _sfor stator phase voltage peak value, ω _r, ω ₁be respectively rotor speed angular velocity of rotation and synchronous rotary angular speed

By resistance R ₀be taken as crow bar resistance R _cBminimum value R _cBmin, by resistance R ₁be taken as crow bar resistance R _cBmaximum and the difference of minimum value, i.e. R ₀=R _cBmin, R ₁=R _cBmax-R _cBmin.Now, crow bar resistance can be got in theory from R _cBminto R _cBmaxdifferent value.

The meaning that above-described change resistance signal produces formula is:

(for describing the problem more easily, note ${\mathrm{\&eta;}}_1=\mathrm{\&alpha;}\&times;\frac{{\left|I_r\right|}_{\max }-I_N}{I_N},{\mathrm{\&eta;}}_2=(1-\mathrm{\&alpha;})\&times;\frac{V_{\mathrm{dc}\_\mathrm{high}}-V_{\mathrm{dc}}}{V_N},$ There is η=η ₁+ η ₂)

There is moment and afterwards very little following period of time in low-voltage, three-phase rotor current maximum amplitude | I _r| _maxupper punch obtains very fast, and DC bus-bar voltage V _dcrise comparatively speaking slowly, now η ₁, η ₂be larger on the occasion of (respectively with respect to the η with after-stage ₁, η ₂value), variable resistor signal η=η ₁+ η ₂for more greatly on the occasion of, i.e. equivalence drops into the crow bar resistance of larger resistance, has effectively suppressed the large impact of crossing of rotor current; Crow bar protective device was devoted oneself to work after a period of time, three-phase rotor current maximum amplitude | I _r| _maxexisting decay, and DC bus-bar voltage V _dcunder the dc-link capacitance charge effects effect of accumulation, rise to higher value, now η ₁, η ₂with respect to all reducing to some extent previous stage, η=η ₁+ η ₂also less for previous stage, i.e. equivalence drops into the crow bar resistance of less resistance, accelerates three-phase rotor current maximum amplitude | I _r| _maxdecay, restriction DC bus-bar voltage too fast rising.

The device and method that double-fed induction wind driven generator system low-voltage provided by the present invention passes through, can fluctuate little in the situation that in DC bus-bar voltage, restrain preferably the impact of rotor current, and quickly rotor current is decayed in safe range, effectively protect rotor-exciting converter, reduced the transient state of electrical network and mechanical system is impacted; The collaborative reactive power compensation of rotor-side converter and grid side converter during simultaneously falling by line voltage, has effectively assisted safety and stability and the recovery of line voltage.

3. embodiment

Carry out control effect analysis of the present invention with the research of the commercial double-fed induction wind driven generator of a 1.5MW below.Motor stator rated voltage 690V, specified DC bus-bar voltage 1050V.Before electric network fault, DFIG is with rated power operation, 1800 revs/min of rotating speeds (1.2pu), and it is 0.84pu (now system send total active power be 1pu) that stator sends active power, sending reactive power is 0.While moving to 0.3s, line voltage rapid drawdown to 15%, continues 300ms.

Can be seen by Fig. 4-Figure 10, adopt low-voltage ride-through method of the present invention, stator and rotor current peak value can be controlled within the scope of 2 times of peak current ratings, and electromagnetic torque pulsation is less, DC bus-bar voltage fluctuation is less, in safe range, and can recover very soon set-point, electromagnetic impact and mechanical shock that visible generator causes system are all less.Simultaneously, because grid side converter in failure process and rotor-side converter all provide certain reactive power support to electrical network, line voltage has had lifting to a certain degree, is conducive to the recovery of line voltage.

Control waveform by Figure 11-Figure 13 can find out, if adopt single little value crow bar resistance, rotor current peak value and electromagnetic torque all can rush to higher value, can cause larger infringement to system; If adopt single large value crow bar resistance, as shown in Figure 14-Figure 16, DC bus-bar voltage can be raised to too high value; And it is of the present invention while regulating in real time the low-voltage ride-through method of crow bar resistance based on resistance when adopting, can fluctuate little in the situation that in DC bus-bar voltage, limit preferably rotor current peak value and electromagnetic torque fluctuation, obtained good low voltage crossing effect, referring to figure Figure 17-Figure 19.

The method regulating in real time based on crow bar resistance of the present invention, it is according to being these two most important amounts of embodiment transient process of detection rotor electric current and DC bus-bar voltage, therefore can be in office under what fault condition, all find suitable crow bar resistance variation tendency, can fluctuate little in the situation that in DC bus-bar voltage, carry out the adjusting of crow bar resistance according to the situation of change of rotor current, restrain preferably the impact of rotor current, and quickly rotor current is decayed in safe range, effectively protect rotor-exciting converter, reduce the transient state of electrical network and mechanical system has been impacted, the collaborative reactive power compensation of rotor-side converter and grid side converter during simultaneously falling by line voltage, has effectively assisted safety and stability and the recovery of line voltage.

Claims (2)

1. the method that double-fed induction wind driven generator system low-voltage passes through, on the device that the method is passed through at double-fed induction wind driven generator system low-voltage, realize, the device that described double-fed induction wind driven generator system low-voltage passes through is mainly made up of double-fed induction wind driven generator, rotor-exciting converter, crow bar protective device, du/dt inductance, LCL filter and system controller; Wherein, the rotor three-phase winding of double-fed induction wind driven generator is connected with rotor-exciting converter one side by du/dt inductance, and the opposite side of rotor-exciting converter is connected to electrical network by LCL filter and grid-connected transformer; The three-phase input end of crow bar protective device is connected with the rotor three-phase winding of double-fed induction wind driven generator by du/dt inductance, on connecting, forms relation in parallel with rotor-exciting converter; System controller is connected with crow bar protective device with rotor-exciting converter; Rotor-exciting converter is made up of grid side converter, dc-link capacitance and rotor-side converter; It is characterized in that, the method comprises the following steps:

(1) in the time that electrical network low voltage causes double-fed induction wind driven generator rotor current to rise to being equal to or greater than capping value, system controller blocks rotor-side converter pulses conducting crow bar protective device switch, drop into crow bar protective device, the active power instruction of rotor-side converter is made as to zero simultaneously, and the input of rotor current ring pi regulator integration item is made as to zero;

(2) after crow bar protective device switch conduction, grid side converter is meeting outside necessary active power demand, and trying one's best provides reactive power support to electrical network; Simultaneously by the real-time adjusting to crow bar equivalent resistance resistance, fluctuate little in the situation that in DC bus-bar voltage, restrain preferably the impact of rotor current, and make quickly rotor current decay in safe range, thereby obtain comparatively ideal low voltage crossing performance;

(3) when double-fed induction wind driven generator rotor current decays to while being less than or equal to preset lower limit, system controller turn-offs crow bar protective device switch and excises crow bar protective device, open rotor-side converter pulses simultaneously, rotor-side converter is resumed work and rapidly for electrical network provides certain reactive power, is assisted power system restoration;

(4) line voltage recover and crow bar protective device cut after; the input of rotor current ring pi regulator integration item is reverted to the difference of instruction current and feedback current; grid side converter slowly recovers rated reactive power instruction; rotor-side converter slowly recovers rated reactive power instruction and active power instruction simultaneously, and system is recovered specified running status subsequently.

2. the method that double-fed induction wind driven generator system low-voltage according to claim 1 passes through, is characterized in that, described step (2) realizes by following sub-step:

(2.1) according to the specified rotor current amplitude of double-fed induction wind driven generator system and the maximum DC bus-bar voltage that allows, determine the function f that is respectively take three-phase rotor current maximum amplitude and DC bus-bar voltage as variable (| I _r| _max) and f (V _dc);

Function f (| I _r| _max) and f (V _dc) be respectively | I _r| _maxand V _dcpositive relationship linear function and the negative linear function that is related to,

$f\left(\right|I_r{|}_{\max })=\frac{|I_r{|}_{\max }-I_N}{I_N}$

$f\left(V_{\mathrm{dc}}\right)=\frac{V_{\mathrm{dc}\_\mathrm{safe}}-V_{\mathrm{dc}}}{V_N};$

Wherein, | I _r| _maxfor the maximum of the three-phase rotor current signal recording from du/dt inductance and rotor-exciting converter link taking absolute value respectively, i.e. three-phase rotor current maximum amplitude, I _nfor specified rotor current amplitude,

V _{dc_safe}for maximum allows DC bus-bar voltage, V _dcfor the DC bus-bar voltage recording from rotor-exciting converter dc-link capacitance two ends, V _nfor specified DC bus-bar voltage;

(2.2) adopt weighting method to function f (| I _r| _max) and f (V _dc) carry out comprehensive calculation process, obtain becoming resistance signal;

Becoming resistance signal can be obtained by following formula:

$\begin{array}{c}\mathrm{\&eta;}=f\left(\right|I_r{|}_{\max },V_{\mathrm{dc}})=\mathrm{\&alpha;}\&times;f\left(\right|I_r{|}_{\max })+(1-\mathrm{\&alpha;})\&times;f\left(V_{\mathrm{dc}}\right)\\ =\mathrm{\&alpha;}\&times;\frac{|I_r{|}_{\max }-I_N}{I_N}+(1-\mathrm{\&alpha;})\&times;\frac{V_{\mathrm{dc}\_\mathrm{safe}}-V_{\mathrm{dc}}}{V_N}\end{array};$

Wherein, α is the weight coefficient of considering rotor current impact;

(2.3) result above-mentioned power transformation resistance calculated signals formula being obtained is done output violent change, and then obtain equivalent crow bar resistance, realize the real-time adjusting of crow bar resistance: power transformation is hindered to the result that calculated signals formula obtains and do output violent change, bottoming value is 0, output higher limit is 1, obtains final for calculating the change resistance signal η of equivalent crow bar resistance ₀, and then obtain equivalent crow bar resistance R _cBresistance be:

R _CB=R ₀+η ₀×R ₁；

Wherein, crow bar resistance is by resistance R ₀with the resistance R that is parallel with chopper ₁resistance branch in series, it is as follows that its resistance is chosen process:

First when, first the design of crow bar resistance will meet fault generation, the maximum of rotor current is less than the safe current I that device allows _safe, that is:

$\frac{{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_1}\frac{U_s}{\sqrt{{\left({\mathrm{\&omega;}}_r{L}_{\mathrm{\&sigma;}}\right)}^2+R_{\mathrm{CB}}^2}}<I_{\mathrm{safe}};$

Formula can calculate crow bar resistance R thus _cBminimum value R _cBmin, that is:

$R_{\mathrm{CB}\min }=\frac{{\mathrm{\&omega;}}_r}{I_{\mathrm{safe}}}\sqrt{{\left(\frac{U_s}{{\mathrm{\&omega;}}_1}\right)}^2-{\left(L_{\mathrm{\&sigma;}}{I}_{\mathrm{safe}}\right)}^2};$

Secondly, the ohmically voltage of crow bar should be less than the magnitude of voltage V that DC bus can bear _{dc_safe}, that is:

$\frac{{\mathrm{\&omega;}}_r}{{\mathrm{\&omega;}}_1}\frac{\sqrt{3}{R}_{\mathrm{CB}}{U}_s}{\sqrt{{\left({\mathrm{\&omega;}}_r{L}_{\mathrm{\&sigma;}}\right)}^2+R_{\mathrm{CB}}^2}}<V_{\mathrm{dc}\_\mathrm{safe}};$

Formula can calculate crow bar resistance R thus _cBmaximum R _cBmax:

$R_{\mathrm{CB}\max }=\frac{V_{\mathrm{dc}\_\mathrm{safe}}{\mathrm{\&omega;}}_r{L}_{\mathrm{\&sigma;}}}{\sqrt{3{(U_s{\mathrm{\&omega;}}_r/{\mathrm{\&omega;}}_1)}^2-V_{\mathrm{dc}\_\mathrm{safe}}^2}};$

In above-mentioned four formulas, L _σ=L _{σ s}+ L _{σ r}for single-phase total leakage inductance, L _{σ s}, L _{σ r}be respectively stator phase leakage inductance and rotor phase leakage inductance, U _sfor stator phase voltage peak value, ω _r, ω ₁be respectively rotor angular speed and synchronous rotary angular speed;

By resistance R ₀be taken as crow bar resistance R _cBminimum value R _cBmin, by resistance R ₁be taken as crow bar resistance R _cBmaximum and the difference of minimum value, i.e. R ₀=R _cBmin, R ₁=R _cBmax-R _cBmin; Now, crow bar resistance can be got in theory from R _cBminto R _cBmaxdifferent value.

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